An amorphous semiconductor film made of amorphous silicon, for example, and formed by the glow discharge decomposition of material gases can be created easily in a large area because it grows in a gaseous phase, and can be used as a photoelectric conversion film for low-cost solar cells. Constructions that are well known to draw out electric power efficiently from such large-area amorphous solar cells may include those shown in FIGS. 4 and 5, which connect several solar cells in series. In FIG. 4, transparent electrodes 41, 42, 43 consisting of thin-films made of such transparent conductive materials as tin oxide, ITO and ZnO, are formed in strips on a translucent substrate 11 made of glass, transparent polymer films, or the like, over which amorphous semiconductor layer regions 31, 32, 33 are formed as photoelectric force generating parts, and thereafter metallic electrodes 21, 22, 23 made of metallic films such as Al and Ag are formed thereover. Combinations of the transparent electrode 41, the amorphous semiconductor layer 31, and the metallic electrode 21, and combinations of the transparent electrode 42, the amorphous semiconductor layer 32, and the metallic electrode 22 make up the individual cells. Patterns for both the electrodes and amorphous semiconductor layers are formed so that extended portions 51, 52, 53- of the metallic electrodes in one cell contact the edge of a transparent electrode on an adjoining cell, and these cells are then connected in series.
The solar cell shown in FIG. 4 generates power by light admitted through the substrate 11, while the solar cell shown in FIG. 5 generates power by light admitted from the side opposite the substrate. In the latter solar cells, metallic electrodes 21, 22, 23 made of Al and Ag are formed in strips on an insulating substrate 12 comprising a glass plate, polymer film, or metallic film which is covered with an insulating film, over which thin-film semiconductor layer regions 31, 32, 33 are formed, and then the transparent electrodes 41, 42, 43 made of tin oxide, ITO, or ZnO are formed in strips and several cells are connected in series in a manner similar to the above.
The series connection structure of these solar cells is most commonly formed by patterning each layer using a laser-scribing process, each time a layer is deposited on the substrate.
One of the purposes of this type of series connection structure in large-area solar cells is to obtain high output voltage from one such large-area solar cell. Another more basic purpose is to reduce the joule loss in transparent electrodes. To explain, if one cell of the solar cells is formed on the entire surface of a substrate without forming the series connection structure, generated carriers may migrate over a long distance in the transparent electrode and the metallic electrode on the rear side down to a lead take-out point disposed at the end of a solar cell. The metallic electrode generally has low resistance. As a result, joule loss caused by the current flowing through the metallic electrode may be neglected. However, sheet resistance in the transparent conductive thin-film may normally be as large as 5 to 30 .OMEGA. per square, hence joule loss caused by current flowing over a long distance in the transparent electrode layer cannot be disregarded. For this reason, conventional technology usually disperses a large-area solar cell into several strip-formed cells, and constructs these cells with a width from 4 mm to 20 mm.
However, it is also known to provide a system structured to have with a large number of solar cells, whereby it is not necessary to generate high output voltage from one large-area solar cell. In such cases, the series connection structure causes the following problems. One problem is that, if a large-area solar cell is so structured that it is split into several cells, linear dead spaces that do not contribute to power generation, that is, spaces 51, 52, 53 in FIGS. 4 and 5 are created between the cells. These dead spaces reduce the effective power generation area and therefore, the output from the solar cell. Another problem is that, since the requisite width of the cells has been determined as described above, the optimal number of cells increases as the substrate area increases, inevitably causing the output voltage to be high. If a solar cell with low-voltage output is formed without considering this optimal number of cells, there is a remarkably large loss in the maximum output.
Still another important problem is that the construction as described above generally requires patterning each time each metallic electrode layer, thin-film semiconductor layer, and transparent electrode layer is formed, which makes the manufacturing process complex. Moreover, unless ultra-fine patterning is carried out with sufficient positional accuracy, the ineffective area required for the series connection which does not contribute to power generation, increases, thereby reducing the efficiency. Furthermore, to pattern the thin-film semiconductor layer and the metallic electrode layer in the case of FIG. 4, and the thin-film semiconductor layer and the transparent electrode layer in the case of FIG. 5, it is necessary to cut the layers so that the layer beneath a particular layer is not damaged, which is difficult in the case of patterning that uses laser beams. However, adopting a wet process such as photoetching causes the manufacturing process to be complex, which makes it difficult to reduce manufacturing costs.